The present application relates to displays suitably applied to e.g. liquid crystal displays and electro-luminescence (EL) displays, and particularly to a display technique that allows light reception in parallel to light emission.
In an existing display such as a television receiver having on its display screen a touch panel that can be operated through contact to its screen, the touch panel is placed on the display screen as a separate body from the display.
Examples of the configuration employing a touch panel as a separate body include a configuration in which a transparent thin input detection device is attached onto the display screen. This device is a touch sensor employing an electrically conductive film. Types of the device include a pressure-sensitive type device to detect a pressure, an electrostatic capacitance type device to detect electrostatic capacitances, which change depending on contact with a human body. Furthermore, the types include also a device called an electromagnetic induction type device in which positions are input with use of a special pen. In these devices, one separate special panel for position detection is laminated on a face of a display panel.
In the display employing a detection panel attached onto its display panel, the principle of touch detection is simple. However, the display inevitably involves lowering of the display quality because any member is laminated on its display panel. Furthermore, detecting capacitance changes is a main method for detection in the display, which makes it difficult to detect inputs of two or more positions simultaneously.
As a touch panel system employing no additional panel on a display panel, an optical touch panel system is available. In this system, combinations of a light-emitting element (e.g., light emitting diode) and a phototransistor are arranged across the entire panel, and positions are detected based on light shielding by a finger or the like. In such an optical system, no deterioration of the display quality occurs. However, large-scale devices need to be provided around the display, which makes this optical system unsuitable for use in portable apparatuses.
In order to solve disadvantages in these existing touch panels, in recent years, there has been proposed a configuration in which the screen itself of a display is allowed to serve as a touch panel without provision of a separate touch panel. Japanese Patent Laid-open No. 2004-127272 discloses such a display that implements light emission and light reception in parallel.
As an example of the display that implements light emission and light reception in parallel, the following display has been proposed. Specifically, in the display, displaying by display (light-emitting) elements for image displaying, arranged on a display plane formed as e.g. a liquid crystal display, is intermittently implemented. Furthermore, in the period during which the displaying (light emission) is temporarily stopped, light-receiving elements disposed adjacent to the light-emitting elements receive light, so that charges dependent upon the received light are accumulated in the light-receiving elements. In addition, a backlight, which is necessary for a liquid crystal display, is repeatedly turned on and off with being associated with the displaying and the light reception. Alternatively, in the case of an EL display, a light-emitting element itself can be used as a light-receiving element, and the period during which light emission by the light-emitting element is temporarily stopped is defined as a light reception period.
However, in the already proposed display that implements light emission and light reception in parallel, for detection of contact to its screen, there is a need to drive light-receiving elements adjacent to light-emitting elements (or drive light-emitting elements so that they serve as light-receiving elements during a light emission pause period) and detect outputs from the light-receiving elements. Therefore, this display involves a problem of higher power consumption than that of a display that implements only light emission.
In a liquid crystal display requiring a backlight in particular, in order to enhance the accuracy of detection of received light, data of the difference between light received in the backlight-ON state and light received in the backlight-OFF state is often obtained so that received light is detected from the difference data. However, in the configuration that needs lighting of a backlight also for light reception, the backlight needs to be turned on even in a period during which displaying is unnecessary, which problematically leads to extra power consumption.